1. Field of the Invention
This invention relates to a device for protecting electrical circuits against static electricity and more particularly to a static electricity discharging device for use in a switch operating device for electrical equipment such as audio equipment.
2. Background
For example, many switches are used in electrical equipment such as audio equipment, such as amplifiers and tape decks. Such switches are operated by respective push buttons mounted on a front panel of the equipment.
One conventional switch operating device shown in FIG. 1 comprises a push button 2 extending outwardly of a front panel 1 through an aperture 1A formed therethrough, the front panel 1 and the push button 2 being made of plastic. A rear portion 2A of the push button 2 extends through an elastic member 3 made of a cushioning material such as sponge which is disposed between a flange 2B of the push button 2 and a frame wall 7. The flange 2B of the button 2 defines the height of a portion of the push button 2, which projects the front panel 1. The elastic force of the elastic member 3 is supplied to the button 2 through the flange 2B so that the button 2 returns to an original position immediately after it is pushed. The rear portion 2A of the push button 2 is held in contact with an actuator projection 5A of a switch 5, the switch 5 being mounted on a printed circuit board 4. The switch 5 and actuator projection 5A may be made of plastic. With this construction, the switch 5 is operated by pushing the push button 2 against the elastic force or resiliency of the elastic member 3.
The above conventional switch operating device is not provided with any means for protecting the device against external static electricity. Therefore, when pushing the push button 2 to operate the switch 5, the static electricity charged in the body of the operator is sometimes applied to the printed circuit board 4 thereby destroying the circuit, which is known as a static destroy.
To overcome the above difficulty, as shown in FIGS. 2 and 3, it has been proposed to use leaf springs 6 made of metal instead of the above-mentioned elastic member 3 made of a cushioning material, the lead springs 6 being formed integrally with a frame 8. The frame 8 has a bent portion 8a so as to prevent the leaf springs from warping and bending. The The leaf spring 6 serves to produce the required resilient force and also to lead the static electricity to the ground or earth. However, with this construction, the use of the metal leaf springs 6 is indispensable. However, since in fact , a plurality of push buttons 2 are provided on the frame wall 7, it was necessary to prepare many leaf springs. Therefore, the number of component parts is increased. Further, an additional manufacturing operation of shaping the leaf springs 6 to a predetermined configuration is required. This increases the cost of the switch operating device.